1. Field of the Invention
This invention relates to earth boring bits, lubricated with a system which includes a hydrostatic pressure compensator to balance the internal pressure of the lubricant inside the bit with the hydrostatic pressure of a liquid drilling fluid that surrounds the bit during drilling. In this combination, the specific improvement relates to the seal assembly between each cutter and bearing shaft which confines lubricant within, and excludes contaminates from, the lubrication system.
2. Background Information
Background information and prior art are provided in the above patent, beneficial in appreciating the present invention. The preferred embodiment disclosed in the above patent utilizes a pair of rigid face seals positioned in a seal groove, including a pair of resilient energizer rings, preferably of the O-ring type. The dimensional relationships of the sealing components and the groove result in greater axial movement of the rigid face seals than the associated cutter.
As a bit rotates during drilling, its cutters move axially, or with a rocking motion, on the bearing shafts because of the clearances and normal manufacturing tolerances. Some clearances are necessary to assemble the cutters on the shafts. Axial and radial cutter movements which results from the clearance between cutter and shaft causes rapid pressure variations in the lubricant, or more accurately, volume charges in the lubricant in the vicinity of each seal. In the preferred embodiment of the above related patent, the rigid face seals may move axially a distance greater than the axial cutter movement by a ratio of about 1.88 to one.